I love Monument Valley. It's an award-winning game that people love on both Android and iOS. We also recommend Monument Valley 2. The graphics are crisp, sharp and pretty, all while being simple at the same time.
It's a puzzle-solving game, one that will stress you out and calm you down at the same time. This is a great way to relax if you're nervous while flying, or just want to pass the time. It's not actually stressful, but you'll want to beat each level. Manipulate impossible architectures and slowly but surely let the princess find her way home. Then, you win.
It has won more awards than any game in recent memory and continues to get better. We're big fans of the second release, but I still play the original when I travel.